Topics

Output power

brad martin
 

I found this image of power out on different bands from Tim (WB7UVH) and wondering is this about average on power out that everyone is seeing. I’m trying to whip up a adhoc power meter using an Arduino mega I have laying about so was going to use the numbers in there as a baseline until I can get my hands on a real power meter to calibrate properly. 

Thank you
Brad
Kg5spr 

brad martin
 

Just realized i forgot to attach


On Tue, Jun 19, 2018 at 7:58 PM brad martin <emclinux@...> wrote:
I found this image of power out on different bands from Tim (WB7UVH) and wondering is this about average on power out that everyone is seeing. I’m trying to whip up a adhoc power meter using an Arduino mega I have laying about so was going to use the numbers in there as a baseline until I can get my hands on a real power meter to calibrate properly. 

Thank you
Brad
Kg5spr 

Doug W
 

Here's mine for another reference.  I did not record the frequencies but they were all tested tx'ing FT8 so you could look them up if needed.  12v input.
  watts
80m 9.36
40m 8.12
30m 4.67
20m 4.16
17m 2.66
15m 1.88
12m 1.64
10m 1.32

--
www.bitxmap.com

ajparent1/kb1gmx
 

You don't need an Arduino to measure power.

You need a load (10W) such as six 300 ohm 2 watt metal film resistors in parallel
and a 1n5711 diode to rectify the RF.    Look around the net as that is an easy build.
Read the voltage with a voltmeter (analog or digital).

I built mine a large fraction of a century ago small box, connector, load as described,
and a diode with binding posts for connecting the meter.  

Calibration, the easy was is apply known DC voltages across the load and note the 
DC meter reading after the diode.  Do this for many points and make a chart of 
power in for voltage out.

Calculate power in:
The power is: DCin^2/50=  (DC applied voltage squared then divide by 50). 
That works well enough to get to better than 5% accurate at least.

No need to use a microprocessor unless you have time to burn.
as then you need a opamp to linearize the diode and scale the input.

Allison

Doug W
 

On Wed, Jun 20, 2018 at 08:36 am, ajparent1/KB1GMX wrote:
You need a load (10W) such as six 300 ohm 2 watt metal film resistors in parallel
and a 1n5711 diode to rectify the RF.
If anyone is looking for a kit here what I have https://qrpguys.com/12w-dummy-load-power-meter  sure you could piece together the parts for a little less but I didn't have everything on hand.
 
--
www.bitxmap.com

Jack, W8TEE
 

The DL I mentioned the other day has this resistor pack:

Inline image

in it, which has 20 3W 1000Ω resistors sitting in a bath of mineral oil. Overkill by a factor of 20 for QRP, but great if you work both QRP and a standard 100W transceiver. You could build it without the OLED and Nano watt meter, but for $20 for everything, why not? (Details will be in Nov, 2018, QST.)

Jack, W8TEE


On Wednesday, June 20, 2018, 11:54:49 AM EDT, Doug W <dougwilner@...> wrote:


On Wed, Jun 20, 2018 at 08:36 am, ajparent1/KB1GMX wrote:
You need a load (10W) such as six 300 ohm 2 watt metal film resistors in parallel
and a 1n5711 diode to rectify the RF.
If anyone is looking for a kit here what I have https://qrpguys.com/12w-dummy-load-power-meter  sure you could piece together the parts for a little less but I didn't have everything on hand.
 
--
www.bitxmap.com

Doug W
 

On Wed, Jun 20, 2018 at 09:04 am, Jack Purdum wrote:
20 3W 1000Ω resistors sitting in a bath of mineral oil
when I saw that in your book I remember thinking if my boiler quits in the middle of winter that would make a nice backup!
 
--
www.bitxmap.com

Jack, W8TEE
 

HA! We ran 200W into it for about 5 minutes and, while it could probably make French Fries, nothing was damaged. Still, we rate it at 150W for use as a DL or a parttime hand-warmer otherwise.

Jack, W8TEE

On Wednesday, June 20, 2018, 12:21:03 PM EDT, Doug W <dougwilner@...> wrote:


On Wed, Jun 20, 2018 at 09:04 am, Jack Purdum wrote:
20 3W 1000Ω resistors sitting in a bath of mineral oil
when I saw that in your book I remember thinking if my boiler quits in the middle of winter that would make a nice backup!
 
--
www.bitxmap.com

rcbuck@...
 

The dummy load looks identical to the one K4EAA describes on his website. His has a couple of diodes to output the voltage from the load. Power can be calculated by measuring the output voltage.

Ray
AB7HE

Jerry Gaffke
 

The $10 qrpguys dummy load looks good, about what Allison was suggesting except that 
they include a cap across the meter leads, Allison's scheme assumes the meter itself
provides the needed capacitance.
Their manual is worth looking over:  https://qrpguys.com/12w-dummy-load-power-meter
The qrpguys suggest calculating watts using   VoltsPk * VoltsPk / 100
where VoltsPk is half of the peak-to-peak voltage across the entire waveform.
That comes from   VoltsRMS * AmpsRMS = VoltsPk*0.707 * (VoltsPk*0.707 / Ohms)

On Mouser, you can get the needed parts for around a dollar if $10 is over your budget.
    1x 511-1N5711   and 4x 283-200-RC
That Xicon 3W 200 ohm metal film resistor has many siblings at other resistance values.
If you get 20 of them at 1k in parallel, that's 50 ohms able to dissipate 60 watts in air.
Or a couple hundred in Jack's french fry oil. 
Though the 1n5711 diode will blow at reverse voltages in excess of 70v,
so max peak-to-peak voltage of the RF into 50 ohms is 70 volts, Watts is 70/2 * 70/2 / 100 = 12.25 Watts
when using the 1n5711.

The 1n5711 will drop around 0.2v at the currents involved.
Let's assume the meter reads 1 volt DC from the 1n5711, how much RF power?
  1 * 1 /100 = 10mW
If we correct for the 0.2v drop across the 1n5711, we find that the power is actually
  1.2 * 1.2 / 100 = 14.4 mW
which is close enough.  At the 1 watt level we are off by only 4%.
You could correct for most of this by simply adding 0.2v to the meter reading.
I doubt you need to calibrate anything.

No DC is present in the transmitter output, so no blocking cap is required.


On a related note, the RF diode probes that Arv points to in post 52474 are rather odd
    http://www.qsl.net/g3pto/probe.html
though as he notes, "There are many variations on this design."
First one has the diode reversed from most, so the meter will see a negative voltage,
and good luck getting a GEX66 diode.  Otherwise, that seems a good design.
Second one has a a voltage doubler, though it also has two diode drops so no real gain in sensitivity or accuracy.
These diode probes are mentioned in most every radio handbook of the last 100 years.
And seldom explained.

Here's a diode RF probe that's more typical:  http://www.n5ese.com/rfprobe1.htm
The 1n34a diode is hard to get, many vendors just ship a Schottky.  I'd use a 1n5711. 
For those that don't want to follow the link, it's a 0.01 uF cap in series with the probe tip,
a 1n34a diode from ground to the other end of that cap, and a series 4.7 meg resistor from
that cap + diode junction out to the meter.  Simple.  But confusing as hell.

The cap blocks any DC coming in on the probe tip, but is zero ohms to AC.
So the cap + diode junction has an AC waveform equivalent to what is being probed.
The diode conducts whenever that junction goes below ground, so the bottom of that AC waveform
will have a bottom tip a diode drop below ground.  The average voltage of that AC waveform
will be about equal to the peak AC voltage at the probe tip.  The 4.7 meg resistor plus the stray 
capacitance inside the meter form a low pass filter, so the meter sees a DC voltage equal
to the peak AC voltage at the probe tip.  Many meters present an 11 ohm load to our RF probe,
so voltage is attenuated down to  11/(4.7+11) = 0.7 of the peak voltage, and the meter reads
something approximating the RMS voltage of the AC assuming the AC is a sine wave.

I have these issues with the N5ESE probe:
1)   Not all meters are 11 meg
2)   Not all waveforms we look at are sine waves
3)   Output capacitance must be included when driving something like a Nano analog pin
4)   The dependence on meter input resistance and stray capacitance hides some complexity that few will ever figure out.

I'd go with the N5ESE circuit, except:
a)  Use the cheap and easily available 1n5711.  (Or BAT54S)
b)  Reduce the 4.7 meg to less than one tenth of the meter impedance so this reads honest peak voltages.
c)  Add a 0.01uF cap from output to ground to make that RC filter explicit.

We should standardize on something like that, feed it into A7  (Atmel claims a 100 meg input impedance)
Whenever anybody has a question about where between mike and antenna their uBitx is failing,
we will have a common instrument to debug it.  And hopefully get common results.

Oh, and also standardize on that Harbor Freight DVM.   ;-)

Jerry, KE7ER



On Wed, Jun 20, 2018 at 08:54 am, Doug W wrote:
On Wed, Jun 20, 2018 at 08:36 am, ajparent1/KB1GMX wrote:
You need a load (10W) such as six 300 ohm 2 watt metal film resistors in parallel
and a 1n5711 diode to rectify the RF.
If anyone is looking for a kit here what I have https://qrpguys.com/12w-dummy-load-power-meter  sure you could piece together the parts for a little less but I didn't have everything on hand.
 

Peter Aiea
 

Same idea for qrp dummy load. Easy to add a diode and cap for voltage measurement and power calculation.


On Wed, Jun 20, 2018, 11:03 <rcbuck@...> wrote:
The dummy load looks identical to the one K4EAA describes on his website. His has a couple of diodes to output the voltage from the load. Power can be calculated by measuring the output voltage.

Ray
AB7HE

Jack, W8TEE
 

True, there's nothing new about the design and something very similar appeared in Arduino Projects for Amateur Radio. About the only twist is the addition of the small OLED display.

Jack, W8TEE

On Wednesday, June 20, 2018, 2:03:36 PM EDT, rcbuck@... <rcbuck@...> wrote:


The dummy load looks identical to the one K4EAA describes on his website. His has a couple of diodes to output the voltage from the load. Power can be calculated by measuring the output voltage.

Ray
AB7HE

Jack, W8TEE
 

We use a BAV21 diode in our design, which is rated at 250V.

Jack, W8TEE

On Wednesday, June 20, 2018, 3:16:49 PM EDT, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:


The $10 qrpguys dummy load looks good, about what Allison was suggesting except that 
they include a cap across the meter leads, Allison's scheme assumes the meter itself
provides the needed capacitance.
Their manual is worth looking over:  https://qrpguys.com/12w-dummy-load-power-meter
The qrpguys suggest calculating watts using   VoltsPk * VoltsPk / 100
where VoltsPk is half of the peak-to-peak voltage across the entire waveform.
That comes from   VoltsRMS * AmpsRMS = VoltsPk*0.707 * (VoltsPk*0.707 / Ohms)

On Mouser, you can get the needed parts for around a dollar if $10 is over your budget.
    1x 511-1N5711   and 4x 283-200-RC
That Xicon 3W 200 ohm metal film resistor has many siblings at other resistance values.
If you get 20 of them at 1k in parallel, that's 50 ohms able to dissipate 60 watts in air.
Or a couple hundred in Jack's french fry oil. 
Though the 1n5711 diode will blow at reverse voltages in excess of 70v,
so max peak-to-peak voltage of the RF into 50 ohms is 70 volts, Watts is 70/2 * 70/2 / 100 = 12.25 Watts
when using the 1n5711.

The 1n5711 will drop around 0.2v at the currents involved.
Let's assume the meter reads 1 volt DC from the 1n5711, how much RF power?
  1 * 1 /100 = 10mW
If we correct for the 0.2v drop across the 1n5711, we find that the power is actually
  1.2 * 1.2 / 100 = 14.4 mW
which is close enough.  At the 1 watt level we are off by only 4%.
You could correct for most of this by simply adding 0.2v to the meter reading.
I doubt you need to calibrate anything.

No DC is present in the transmitter output, so no blocking cap is required.


On a related note, the RF diode probes that Arv points to in post 52474 are rather odd
    http://www.qsl.net/g3pto/probe.html
though as he notes, "There are many variations on this design."
First one has the diode reversed from most, so the meter will see a negative voltage,
and good luck getting a GEX66 diode.  Otherwise, that seems a good design.
Second one has a a voltage doubler, though it also has two diode drops so no real gain in sensitivity or accuracy.
These diode probes are mentioned in most every radio handbook of the last 100 years.
And seldom explained.

Here's a diode RF probe that's more typical:  http://www.n5ese.com/rfprobe1.htm
The 1n34a diode is hard to get, many vendors just ship a Schottky.  I'd use a 1n5711. 
For those that don't want to follow the link, it's a 0.01 uF cap in series with the probe tip,
a 1n34a diode from ground to the other end of that cap, and a series 4.7 meg resistor from
that cap + diode junction out to the meter.  Simple.  But confusing as hell.

The cap blocks any DC coming in on the probe tip, but is zero ohms to AC.
So the cap + diode junction has an AC waveform equivalent to what is being probed.
The diode conducts whenever that junction goes below ground, so the bottom of that AC waveform
will have a bottom tip a diode drop below ground.  The average voltage of that AC waveform
will be about equal to the peak AC voltage at the probe tip.  The 4.7 meg resistor plus the stray 
capacitance inside the meter form a low pass filter, so the meter sees a DC voltage equal
to the peak AC voltage at the probe tip.  Many meters present an 11 ohm load to our RF probe,
so voltage is attenuated down to  11/(4.7+11) = 0.7 of the peak voltage, and the meter reads
something approximating the RMS voltage of the AC assuming the AC is a sine wave.

I have these issues with the N5ESE probe:
1)   Not all meters are 11 meg
2)   Not all waveforms we look at are sine waves
3)   Output capacitance must be included when driving something like a Nano analog pin
4)   The dependence on meter input resistance and stray capacitance hides some complexity that few will ever figure out.

I'd go with the N5ESE circuit, except:
a)  Use the cheap and easily available 1n5711.  (Or BAT54S)
b)  Reduce the 4.7 meg to less than one tenth of the meter impedance so this reads honest peak voltages.
c)  Add a 0.01uF cap from output to ground to make that RC filter explicit.

We should standardize on something like that, feed it into A7  (Atmel claims a 100 meg input impedance)
Whenever anybody has a question about where between mike and antenna their uBitx is failing,
we will have a common instrument to debug it.  And hopefully get common results.

Oh, and also standardize on that Harbor Freight DVM.   ;-)

Jerry, KE7ER



On Wed, Jun 20, 2018 at 08:54 am, Doug W wrote:
On Wed, Jun 20, 2018 at 08:36 am, ajparent1/KB1GMX wrote:
You need a load (10W) such as six 300 ohm 2 watt metal film resistors in parallel
and a 1n5711 diode to rectify the RF.
If anyone is looking for a kit here what I have https://qrpguys.com/12w-dummy-load-power-meter  sure you could piece together the parts for a little less but I didn't have everything on hand.
 

Jerry Gaffke
 

The 70v reverse max spec on the 1n5711 need not limit the power you can measure.
Just add a resistive voltage divider to reduce the voltage that the 1n5711 sees.
For example, add a 900 and a 100 ohm resistor in series from the top of the dummy load to ground,
and use the 1n5711 diode detector across the 100 ohm resistor.  Reduces the voltage by 10x
with minimal disturbance to the 50 ohm dummy load.  
Max power is now (10*70/2) * (10*70/2) / 100 = 1225 Watts.
Enough to burn the fries.

Jerry




On Wed, Jun 20, 2018 at 12:16 pm, Jerry Gaffke wrote:
The $10 qrpguys dummy load looks good, about what Allison was suggesting except that 
they include a cap across the meter leads, Allison's scheme assumes the meter itself
provides the needed capacitance.
Their manual is worth looking over:  https://qrpguys.com/12w-dummy-load-power-meter
The qrpguys suggest calculating watts using   VoltsPk * VoltsPk / 100
where VoltsPk is half of the peak-to-peak voltage across the entire waveform.
That comes from   VoltsRMS * AmpsRMS = VoltsPk*0.707 * (VoltsPk*0.707 / Ohms)

On Mouser, you can get the needed parts for around a dollar if $10 is over your budget.
    1x 511-1N5711   and 4x 283-200-RC
That Xicon 3W 200 ohm metal film resistor has many siblings at other resistance values.
If you get 20 of them at 1k in parallel, that's 50 ohms able to dissipate 60 watts in air.
Or a couple hundred in Jack's french fry oil. 
Though the 1n5711 diode will blow at reverse voltages in excess of 70v,
so max peak-to-peak voltage of the RF into 50 ohms is 70 volts, Watts is 70/2 * 70/2 / 100 = 12.25 Watts
when using the 1n5711.

The 1n5711 will drop around 0.2v at the currents involved.
Let's assume the meter reads 1 volt DC from the 1n5711, how much RF power?
  1 * 1 /100 = 10mW
If we correct for the 0.2v drop across the 1n5711, we find that the power is actually
  1.2 * 1.2 / 100 = 14.4 mW
which is close enough.  At the 1 watt level we are off by only 4%.
You could correct for most of this by simply adding 0.2v to the meter reading.
I doubt you need to calibrate anything.

No DC is present in the transmitter output, so no blocking cap is required.


On a related note, the RF diode probes that Arv points to in post 52474 are rather odd
    http://www.qsl.net/g3pto/probe.html
though as he notes, "There are many variations on this design."
First one has the diode reversed from most, so the meter will see a negative voltage,
and good luck getting a GEX66 diode.  Otherwise, that seems a good design.
Second one has a a voltage doubler, though it also has two diode drops so no real gain in sensitivity or accuracy.
These diode probes are mentioned in most every radio handbook of the last 100 years.
And seldom explained.

Here's a diode RF probe that's more typical:  http://www.n5ese.com/rfprobe1.htm
The 1n34a diode is hard to get, many vendors just ship a Schottky.  I'd use a 1n5711. 
For those that don't want to follow the link, it's a 0.01 uF cap in series with the probe tip,
a 1n34a diode from ground to the other end of that cap, and a series 4.7 meg resistor from
that cap + diode junction out to the meter.  Simple.  But confusing as hell.

The cap blocks any DC coming in on the probe tip, but is zero ohms to AC.
So the cap + diode junction has an AC waveform equivalent to what is being probed.
The diode conducts whenever that junction goes below ground, so the bottom of that AC waveform
will have a bottom tip a diode drop below ground.  The average voltage of that AC waveform
will be about equal to the peak AC voltage at the probe tip.  The 4.7 meg resistor plus the stray 
capacitance inside the meter form a low pass filter, so the meter sees a DC voltage equal
to the peak AC voltage at the probe tip.  Many meters present an 11 ohm load to our RF probe,
so voltage is attenuated down to  11/(4.7+11) = 0.7 of the peak voltage, and the meter reads
something approximating the RMS voltage of the AC assuming the AC is a sine wave.

I have these issues with the N5ESE probe:
1)   Not all meters are 11 meg
2)   Not all waveforms we look at are sine waves
3)   Output capacitance must be included when driving something like a Nano analog pin
4)   The dependence on meter input resistance and stray capacitance hides some complexity that few will ever figure out.

I'd go with the N5ESE circuit, except:
a)  Use the cheap and easily available 1n5711.  (Or BAT54S)
b)  Reduce the 4.7 meg to less than one tenth of the meter impedance so this reads honest peak voltages.
c)  Add a 0.01uF cap from output to ground to make that RC filter explicit.

We should standardize on something like that, feed it into A7  (Atmel claims a 100 meg input impedance)
Whenever anybody has a question about where between mike and antenna their uBitx is failing,
we will have a common instrument to debug it.  And hopefully get common results.

Oh, and also standardize on that Harbor Freight DVM.   ;-)

Jerry, KE7ER



On Wed, Jun 20, 2018 at 08:54 am, Doug W wrote:
On Wed, Jun 20, 2018 at 08:36 am, ajparent1/KB1GMX wrote:
You need a load (10W) such as six 300 ohm 2 watt metal film resistors in parallel
and a 1n5711 diode to rectify the RF.
If anyone is looking for a kit here what I have https://qrpguys.com/12w-dummy-load-power-meter  sure you could piece together the parts for a little less but I didn't have everything on hand.
 

 gOn Wed, Jun 20, 2018 at 12:16 pm, Jerry Gaffke wrote:
The $10 qrpguys dummy load looks good, about what Allison was suggesting except that 
they include a cap across the meter leads, Allison's scheme assumes the meter itself
provides the needed capacitance.
Their manual is worth looking over:  https://qrpguys.com/12w-dummy-load-power-meter
The qrpguys suggest calculating watts using   VoltsPk * VoltsPk / 100
where VoltsPk is half of the peak-to-peak voltage across the entire waveform.
That comes from   VoltsRMS * AmpsRMS = VoltsPk*0.707 * (VoltsPk*0.707 / Ohms)

On Mouser, you can get the needed parts for around a dollar if $10 is over your budget.
    1x 511-1N5711   and 4x 283-200-RC
That Xicon 3W 200 ohm metal film resistor has many siblings at other resistance values.
If you get 20 of them at 1k in parallel, that's 50 ohms able to dissipate 60 watts in air.
Or a couple hundred in Jack's french fry oil. 
Though the 1n5711 diode will blow at reverse voltages in excess of 70v,
so max peak-to-peak voltage of the RF into 50 ohms is 70 volts, Watts is 70/2 * 70/2 / 100 = 12.25 Watts
when using the 1n5711.

The 1n5711 will drop around 0.2v at the currents involved.
Let's assume the meter reads 1 volt DC from the 1n5711, how much RF power?
  1 * 1 /100 = 10mW
If we correct for the 0.2v drop across the 1n5711, we find that the power is actually
  1.2 * 1.2 / 100 = 14.4 mW
which is close enough.  At the 1 watt level we are off by only 4%.
You could correct for most of this by simply adding 0.2v to the meter reading.
I doubt you need to calibrate anything.

No DC is present in the transmitter output, so no blocking cap is required.


On a related note, the RF diode probes that Arv points to in post 52474 are rather odd
    http://www.qsl.net/g3pto/probe.html
though as he notes, "There are many variations on this design."
First one has the diode reversed from most, so the meter will see a negative voltage,
and good luck getting a GEX66 diode.  Otherwise, that seems a good design.
Second one has a a voltage doubler, though it also has two diode drops so no real gain in sensitivity or accuracy.
These diode probes are mentioned in most every radio handbook of the last 100 years.
And seldom explained.

Here's a diode RF probe that's more typical:  http://www.n5ese.com/rfprobe1.htm
The 1n34a diode is hard to get, many vendors just ship a Schottky.  I'd use a 1n5711. 
For those that don't want to follow the link, it's a 0.01 uF cap in series with the probe tip,
a 1n34a diode from ground to the other end of that cap, and a series 4.7 meg resistor from
that cap + diode junction out to the meter.  Simple.  But confusing as hell.

The cap blocks any DC coming in on the probe tip, but is zero ohms to AC.
So the cap + diode junction has an AC waveform equivalent to what is being probed.
The diode conducts whenever that junction goes below ground, so the bottom of that AC waveform
will have a bottom tip a diode drop below ground.  The average voltage of that AC waveform
will be about equal to the peak AC voltage at the probe tip.  The 4.7 meg resistor plus the stray 
capacitance inside the meter form a low pass filter, so the meter sees a DC voltage equal
to the peak AC voltage at the probe tip.  Many meters present an 11 ohm load to our RF probe,
so voltage is attenuated down to  11/(4.7+11) = 0.7 of the peak voltage, and the meter reads
something approximating the RMS voltage of the AC assuming the AC is a sine wave.

I have these issues with the N5ESE probe:
1)   Not all meters are 11 meg
2)   Not all waveforms we look at are sine waves
3)   Output capacitance must be included when driving something like a Nano analog pin
4)   The dependence on meter input resistance and stray capacitance hides some complexity that few will ever figure out.

I'd go with the N5ESE circuit, except:
a)  Use the cheap and easily available 1n5711.  (Or BAT54S)
b)  Reduce the 4.7 meg to less than one tenth of the meter impedance so this reads honest peak voltages.
c)  Add a 0.01uF cap from output to ground to make that RC filter explicit.

We should standardize on something like that, feed it into A7  (Atmel claims a 100 meg input impedance)
Whenever anybody has a question about where between mike and antenna their uBitx is failing,
we will have a common instrument to debug it.  And hopefully get common results.

Oh, and also standardize on that Harbor Freight DVM.   ;-)

Jerry, KE7ER



On Wed, Jun 20, 2018 at 08:54 am, Doug W wrote:
On Wed, Jun 20, 2018 at 08:36 am, ajparent1/KB1GMX wrote:
You need a load (10W) such as six 300 ohm 2 watt metal film resistors in parallel
and a 1n5711 diode to rectify the RF.
If anyone is looking for a kit here what I have https://qrpguys.com/12w-dummy-load-power-meter  sure you could piece together the parts for a little less but I didn't have everything on hand.
 

 The 70v reverse voltlt Wed, Jun 20, 2018 at 12:16 pm, Jerry Gaffke wrote:
Though the 1n5711 diode will blow at reverse voltages in excess of 70v,
so max peak-to-peak voltage of the RF into 50 ohms is 70 volts, Watts is 70/2 * 70/2 / 100 = 12.25 Watts
when using the 1n5711.

Jerry Gaffke
 

The BAV21 is not a bad choice for the dummy load dectector.
Very cheap, which is of course my primary criteria.

Forward voltage drop appears to be around 0.5v at 0.1ma from their graphs,
the detector would have a much smaller current going through it.
So should still be able to measure 10mW into the dummy load,
though factoring in that drop to the calculations becomes more important than with the 1n5711. 

I'd still use the 1n5711 for the diode RF probe.

Jerry



On Wed, Jun 20, 2018 at 12:27 pm, Jack Purdum wrote:
We use a BAV21 diode in our design, which is rated at 250V.
 

brad martin
 

Thank you all for the replies. Unfortunately my idea on paper does not look like it’s going to work out based on my experiments last night. My idea was that I have a cb type swr meter and I was going to make it into a digital swr and power meter and well being that it’s not for Hf the output voltage of the meter didn’t line up with output power. .6v on 80, 1v on 40 and 30 and 1.5v on 20. So oh well on that one. I have Arduinos all over the place so using a mega for this is not a loss for me. I almost use them as coasters at this point. I would see a deal on them and get them over the last few years and as far as time goes I always try to make time for my hobbies because life is short right :).

I have seen the dummy load with a cap and diode before and have been planning on adding that to my dummy load as well. When choosing the diode what properties are you looking for?

I have a goal most people would probably say I’m crazy for doing. The plan is that my first HF contact will be done using things I have made, built, or repaired. So far everything I have (power supply, uBITX, antenna, CW paddle, dummy load, and other random stuff) and the swr meter is the only thing I have left that has not has been modified.

73
Brad
KG5SPR

On Wed, Jun 20, 2018 at 3:39 PM Jerry Gaffke via Groups.Io <jgaffke=yahoo.com@groups.io> wrote:
The BAV21 is not a bad choice for the dummy load dectector.
Very cheap, which is of course my primary criteria.

Forward voltage drop appears to be around 0.5v at 0.1ma from their graphs,
the detector would have a much smaller current going through it.
So should still be able to measure 10mW into the dummy load,
though factoring in that drop to the calculations becomes more important than with the 1n5711. 

I'd still use the 1n5711 for the diode RF probe.

Jerry



On Wed, Jun 20, 2018 at 12:27 pm, Jack Purdum wrote:
We use a BAV21 diode in our design, which is rated at 250V.
 

Terry Morris
 

I have a 5 watt dummy load consisting of 5-1 watt carbon resistors, gold band, soldered into a PL-259 connector circa 1970's. It was given to me from an elderly ham, now SK. He learned I was starting the hobby with a QRP kit built HW-9. He told me he tried QRP once but it was too difficult making contacts. Thought I would like the low power heater. I do.

Terry - KB8AMZ
Brimfield Twp, OH  USA
Linux User# 412308, Ubuntu User# 34905


On Wed, Jun 20, 2018 at 7:13 PM brad martin <emclinux@...> wrote:
Thank you all for the replies. Unfortunately my idea on paper does not look like it’s going to work out based on my experiments last night. My idea was that I have a cb type swr meter and I was going to make it into a digital swr and power meter and well being that it’s not for Hf the output voltage of the meter didn’t line up with output power. .6v on 80, 1v on 40 and 30 and 1.5v on 20. So oh well on that one. I have Arduinos all over the place so using a mega for this is not a loss for me. I almost use them as coasters at this point. I would see a deal on them and get them over the last few years and as far as time goes I always try to make time for my hobbies because life is short right :).

I have seen the dummy load with a cap and diode before and have been planning on adding that to my dummy load as well. When choosing the diode what properties are you looking for?

I have a goal most people would probably say I’m crazy for doing. The plan is that my first HF contact will be done using things I have made, built, or repaired. So far everything I have (power supply, uBITX, antenna, CW paddle, dummy load, and other random stuff) and the swr meter is the only thing I have left that has not has been modified.

73
Brad
KG5SPR
On Wed, Jun 20, 2018 at 3:39 PM Jerry Gaffke via Groups.Io <jgaffke=yahoo.com@groups.io> wrote:
The BAV21 is not a bad choice for the dummy load dectector.
Very cheap, which is of course my primary criteria.

Forward voltage drop appears to be around 0.5v at 0.1ma from their graphs,
the detector would have a much smaller current going through it.
So should still be able to measure 10mW into the dummy load,
though factoring in that drop to the calculations becomes more important than with the 1n5711. 

I'd still use the 1n5711 for the diode RF probe.

Jerry



On Wed, Jun 20, 2018 at 12:27 pm, Jack Purdum wrote:
We use a BAV21 diode in our design, which is rated at 250V.